This application relates to a humidifier for delivering a supply of heated, humidified air through an elongated conduit to a mask worn by a patient. The humidifier is designed for use by a patient during sleep to treat chronic breathing disorders such as allergic rhinitis. The relative humidity of the air stream is regulated to ensure that it will not condense to form water droplets within the interior of the conduit.
The air passageways in patients suffering from chronic breathing disorders, such as asthma, rhinitis, bronchitis, sinusitis and the like, are often in a persistent post-traumatically inflamed state. The Applicant has determined that one method of effectively treating such conditions is to supply heated, pollutant-free, humidified air to the patient at night while he or she is sleeping. This enables the patient""s air passageways to rest and partially recover from the inflammation. The patient is then able to resume a normal life during waking hours.
Conventional portable humidifiers designed for home use do not Significantly alter the humidity of the room that they are operating in and are therefore of limited benefit. Moreover, to the extent that such portable humidifiers do increase ambient humidity, they result in undesirable side effects. For example, increased ambient humidity levels may exacerbate rather than alleviate a patient""s respiratory tract inflammation by causing increased growth of mites, fungi or other allergens in the patient""s sleeping environment.
Breathing tents surrounding all or a portion of the patient""s bed for delivering heated, humidified air to the patient during sleep are also well-known in the prior art. However, such tents are not desirable since they often result in overheating of the patient and cause excess perspiration.
A more effective means for raising the humidity of air inhaled by a patient at rest is to deliver humidified air directly to a face mask worn by the patient. Typically, the mask is connected to a bedside humidifier apparatus by an elongate conduit. One problem which has arisen with such devices is the tendency for the humidified air to condense as water vapour within the conduit. The water vapour then drips into the face mask, repeatedly rousing the patient from sleep.
Relative humidity is a percentage expression of the actual water vapour content of a gas as compared to its capacity to carry water at any given temperature. The capacity of a gas to hold water in its vaporous state increases with molecular velocity as the temperature of the gas rises. For example, as the temperature of air drops, its capacity to hold moisture also declines proportionately and hence the relative humidity increases. When the air temperature drops below the dew point, the excess vapour condenses as water droplets. Condensation of water vapour or xe2x80x9ccondensate rainoutxe2x80x9d can result from a drop in the temperature of humidified air as it passes through a conduit, such as a conduit extending between a supply of humidified air and a face mask.
One approach for addressing this problem is to uniformly heat the air travelling through the conduit by means of electric wires wound around the conduit and controlled by a temperature sensor. For example, U.S. Pat. No. 3,638,926 describes a humidification system wherein the tube interconnecting the humidifier and the patient is heated at least partially along its length by means of electric elements embedded within the wall of the tube. The primary drawback of heated wire systems is expense. Heated wire systems, such as those used in hospitals, tend to be about twice as expensive as conventional humidifiers.
Another approach for controlling water vapour condensation is to raise the temperature of the humidified air introduced into the conduit inlet to a temperature above the preferred outlet temperature. The inlet temperature is calibrated to take into account the anticipated heat drop along the length of the conduit and the corresponding increase in relative humidity. For example, in the ""926 patent referred to above, the air leaving the humidifier is preferably at 35.5xc2x0 C. (i.e. approximately body temperature) and is between 85-100% saturated. The air temperature is then increased to 47.8xc2x0 C. to compensate for an anticipated temperature drop of about 10xc2x0 C. along the length of the delivery hose. This avoids condensation of water vapour between the humidifier and the mask worn by the patient.
One drawback of the ""926 system described above is that the humidified air is not heated and maintained at a temperature sufficient to sterilize the air supply to kill all air-borne bacteria or viruses before delivery to the patient. Moreover, the ""926 system is reliant upon the use of supplementary heated wires in the delivery hose to reduce the magnitude of the heat drop.
U.S. Pat. No. 5,558,084, Daniell et al., describes a humidifier having a delivery tube for providing humidified gases to an intubated patient or a face mask worn by a patient. The Daniell et al. humidifier includes temperature sensors for sensing the ambient temperature and the temperature of gas expelled from the humidifier. Electronic control circuitry is provided for adjusting the temperature of the expelled gas depending upon the ambient temperature to minimize condensate rainout in the air delivery tube extending between the humidifier and the face mask. The Daniell et al. humidifier does not include an internal gas supply but rather is designed to connect to a CPAP machine or some other external gas supply. This limits the suitability of the Daniell et al. invention for home use in the treatment of sinusitis and other similar disorders where a large flow rate of humidified gas is not required but where it is important that the air be delivered at consistently high relative humidity. The Daniell et al. invention does not teach the advantages of mixing separate streams of hot humidified air and hot dry air together within the humidifier to achieve a mixed air stream which is discharged from the humidifier by a fan blower at the optimum temperature and relative humidity.
The need has therefore arisen for a humidification system which delivers substantially sterile air to a patient for inhalation during sleep in a cost-effective manner. The air is delivered at a preferred temperature and humidity to avoid the disadvantages of vapour condensation within the air delivery conduit.
In accordance with the invention, an apparatus and method for delivering humidified air through a conduit to a patient for inhalation during sleep is disclosed. The conduit has an inlet connected to a humidifier and an outlet connected to a breathing mask worn by the patient.
The applicant""s apparatus comprises a humidifier having an inlet for receiving a supply of intake air; a first chamber for holding a first volume of the intake air; a second chamber for holding a second volume of the intake air, wherein the second volume of air is passed over the surface of water contained within the second chamber; a heater for heating the water and the second volume of air within the second chamber; a mixing conduit for receiving and mixing together separate first and second streams of air discharged from the first and second chambers respectively; and an adjustable regulator for regulating the amount of the second stream of air passing into the mixing conduit.
Preferably the second chamber is located within the first chamber and the first chamber surrounds the second chamber. The heater is disposed so that it also heats the first volume of air in the first chamber. Advantageously, the first and second air streams are heated to approximately the same temperature. The second container may consist of a container and a removable lid for covering the container, wherein the intake air passes from the first chamber into the second chamber through an opening defined between the container and the lid.
The humidifier preferably includes a first compartment and a second compartment, wherein the first and second chambers are located in the first compartment and wherein the mixing conduit extends from the first compartment into the second compartment. The humidifier also includes an air outlet port connectable to the face mask and a fan mounted in the second compartment for conveying air from the mixing conduit to the air outlet port. Preferably, the first compartment is located above the second compartment and the heater is disposed in a lower portion of the first compartment.
The air inlet consists of a inlet conduit extending through the second compartment into the first compartment. The inlet conduit has an open upper end to discharge the intake air into the first chamber. The second chamber is located between the inlet conduit and the mixing conduit. The inlet conduit and mixing conduit are preferably disposed on opposite sides of the humidifier.
The mixing conduit comprises a first tube having an open upper end in communication with the first chamber and a second tube having an upper portion in communication with the second chamber and a lower portion extending within the first tube. The adjustable regulator comprises a valve for regulating flow of the second air stream into the second tube.
The applicant has also developed a method for delivering humidified air through an unheated conduit to a patient, the conduit having an inlet connected to a humidifier and an outlet connected to a breathing mask worn by the patient. The applicant""s method comprises the steps of:
(a) heating a first volume of air in the humidifier to form a supply of heated dry air;
(b) heating a volume of water in the humidifier and passing a second volume of air over the surface of the water to form a supply of heated moisture-laden air;
(c) adjustably mixing the heated dry air and the moisture-laden air together in the humidifier to form a stream of heated humidified air;
(d) conveying the heated humidified air from the humidifier through the conduit to the mask,
wherein the temperature and relative humidity of the humidified air is adjusted to substantially prevent condensation of the humidified air in the conduit.
Preferably, the temperature of the humidified air while resident within the conduit decreases to less than 40xc2x0 C. and the relative humidity of the humidified air while resident within the conduit increases to greater than 80%.
In an alternative embodiment of the invention, the separate streams of heated dry air and heated moisture-laden air may be mixed in fixed amounts in the mixing conduit and the adjustable regulator may be omitted. The mixing conduit may extend into an upper portion of the first chamber for drawing dry air into the mixing conduit at a relatively high temperature.
A method of treating inflammation of the mucous membranes of the upper respiratory tract of a patient is also disclosed. The method may be used, for example, in the treatment of conditions such as vasomotor rhinitis, seasonal allergic rhinitis, perennial rhinitis and post-influenza cough syndrome. The method comprises the steps of:
(a) providing a portable humidifier apparatus, the apparatus comprising a source of heated humidified air, a face mask and an air delivery tube for delivering the heated humidified air from the humidifier to the face mask;
(b) fitting the face mask over at least the nose of the patient; and
(c) delivering the humidified air from the humidifier to the face mask for a prolonged period of time while the patient is at rest, wherein the humidified air at the face mask is at a temperature within the range of 25-35xc2x0 C. and at a relative humidity exceeding 90%.